Plating tarnish-resistant bright white alloy



United States Patent 3,547,626 PLATING TARNISH-RESISTANT BRIGHT WHITEALLOY Gaetano T. Viglione, Lexington, Mass. (R.D. 1, Amesbury, Mass.01913) No Drawing. Filed July 2, 1968, Ser. No. 741,896

Int. (:1. C22c 17/00 U.S. Cl. 7s-1s1 4 Claims ABSTRACT OF THE DISCLOSUREA plating bath, process and alloy comprising cadmium, silver and nickelfor tarnish-resistant bright silver applications. An alkaline cyanidewater bath is employed. The alloy composition is 50 to 70% by weight ofcadmium, 20 to 31% by weight of silver, balance nickel and impurities.

The present invention relates to electrolytes, electroplating processesand alloys for tarnish-resistant bright silver applications.

A purpose of the invention is to deposit a tarnishresistant bright whitesilver alloy which resembles the noble metals, especially rhodium, butis much more economical.

A further purpose is to plate a tarnish-resistant bright silver alloyfrom an alkaline cyanide water bath containing cadmium ion, silver ionand nickel ion.

A further purpose is to employ in the alkaline cyanide water bath 0.45to 0.55 gram per liter of cadmium ion, 0.112 to 0.138 gram per liter ofsilver ion and 0.675 to 0.825 gram per liter of nickel ion.

A further purpose is to plate from a preferred alkaline cyanide waterbath containing 0.5 gram per liter of cadmium ion, 0.125 gram per literof silver ion and 0.75 gram per liter of nickel ion.

A further purpose is to deposit an alloy of cadmium, silver and nickelin an attractive tarnish-resistant bright rhodium-like deposit which isefiective in coverage and continuity, firmly adherent and resistant tothe forces of deterioration commonly encountered by jewelry for areasonable time.

A further purpose is to produce an alloy having by weight 50 to 70%,preferably 56 to 64% of cadmium, 20 to 31%, preferably 23 to 28% ofsilver and the balance nickel and impurities.

A further purpose is to produce an alloy having by weight 64% cadmium,23% silver and the balance nickel and impurities.

A further purpose is to produce an alloy having by weight 56% cadmium,28% silver and the balance nickel and impurities.

A further purpose is to electroplate at a temperature of 70 to 120 F.

A further purpose is to employ a current density of 5 to 60 amperes persquare foot and preferably to 30 amperes per square foot.

A further purpose is to employ in the cyanide plating bath an adequatequantity of an alkali such as sodium or potassium hydroxide, for example7 to 21 grams per liter.

A further purpose is to electroplate on a base of any of the commonmetals suitable for jewelry and the like, for example steel, copper,brass, and bronze, applying the electroplating of the inventiondirectly, or if desired with intermediate layers, such as copper platingor nickel plating.

Further purposes appear in the specification and in the claims.

3,547,626 Patented Dec. 15, 1970 The present invention is believed tofind its best application in the decorative arts, such as the productionof jewelry, trim for vehicles, decorative surfaces of appliances andmachines, and for corrosion protection where appearance is important, asfor example in instruments and the like.

In the prior art electrodeposited coatings including noble metals suchas rhodium have been extensively developed as embodied in Keitel U.S.Patent 1,779,436, granted Oct. 28, 1930 for Process of Electrodepositingmetals of the Platinum Group; Zschiegner U.S. Patent 1,779,457, grantedOct. 28, 1930, for Electrodeposition of Platinum Metals; Bart U.S.Patent 1,947,180, granted Feb. 13, 1934, for Tarnish-Resisting Silver;and Zimmermann U.S. Patent 1,981,820, granted Nov. 20, 1934, for Processof Electrodepositing Rhodium, Bath and Method of Preparing the Same.

The present invention is concerned with the production of a brightsilver alloy which is much less expensive than a noble metal, but whichhas resistance against tarnishing in the presence of industrialatmospheres of the type encountered in cities, has adequate grainstructure to provide corrosion resistance, has firm adherence to thebase metal, and resistance to scufiing and abrasion of the type likelyto be encountered by jewelry, trim, instrument parts, and the like. Inaddition the alloy of the invention is produced in a singleelectroplating step from a single plating bath at high speed, with apermissibly high deposition rate, and repetitively with good assurancethat the same result will be obtained when all variables are controlled.

The electrodeposited layer can be applied with adequate appearance formany jewelry parts in a matter of a minute or less in order to obtain aplating layer having a thickness of the order of 0.00001 inch, or it canbe applied for the purpose of electroforming in order to make a thickdeposit, having a thickness for example as great as inch or evengreater.

The alloy of the invention lends itslf to deposition on the commonmetals used in making inexpensive jewelry, trim and instrument part,such as carbon and alloy steel, copper and the copper base alloys suchas brass and bronze. The coating of the invention can also be appliedover prior electrodeposited layers which are employed for example forcorrosion protection or to obtain a favorable color background, ascopper or nickel plate on steel.

One of the great advantages of the alloy of the inven tion is that ithas a whiteness and reflectance when polished resembling the platinumgroup metals, and particularly closely similar to that of rhodium plate.

The alloy of the invention resists tarnishing. For example, it has beensubjected to concentrated sodium sulphide solution at F. for 30 minuteswithout any visible impairment in the brightness of the plated surface.

Also, the alloy of the invention resists attack from alkalis inconcentrations which are likely to be encountered by jewelry and trim.

The electroplating according to the invention is carried out in acyanide water bath which of course is maintained alkaline, for exampleby the presence of sodium or potassium hydroxide, for instance in aconcentration of 7 to 21 grams per liter.

The electrolyte has dissolved in it soluble salts providing cadium ion,silver ion and nickel ion. In order to create such ions in the bath, therespective cyanides may be introduced or well known techniques may beused. For example cadmium oxide may be placed in the bath and dissolvedby adding sodium cyanide. It will be evident of course that theconductivity of the bath can be increased if desired by adding sodiumcyanide or other alkaline conducting salts.

It is very desirable to maintain a proper balance of the concentrationof cadmium ion to the concentration of silver ion and the concentrationof nickel ion. Very good results are obtained in an electrolyte having0.45 to 0.55 and preferably 0.5 gram per liter of cadmium ion, 0.112 to0.138 and preferably 0.125 gram per liter of silver ion, and 0.675 to0.825 and preferably 0.75 gram per liter of nickel ion.

The bath temperature can vary widely but good results can be obtained ina temperature range between 70 F. and 120 F. The bath is preferablymaintained at a temperature of 100 F., plus or minus 05 F.

The voltage employed will suitably be in the range of 2 to 12 voltsdirect or unidirectional current. The current density will typicallyvary between 5 and 50 amperes per square foot and preferably between 15and amperes per square foot. For best results an insoluble anode will beemployed, such as stainless steel, platinum, titanium or carbon(graphite). The work will be the cathode, typically mounted by wire oron a rack. The ratio of anode to cathode should not exceed 0.5: 1.

The alloy obtained is an alloy of cadmium, silver and nickel. In itsmore specific aspect it has the following composition in percentage byweight in broad and preferred ranges:

Component; Broad Preferred Cadmium 50-70 23-64 Silver 20-31 23-28 Nickand a small amount of im- M purity Balance Balance The impurity willtypically be 0.5% by weight maximum.

EXAMPLE 1 The following electrolyte bath was made up in water:

Grams per liter The cadmium was added as oxide. The silver was added ascyanide. The nickel was added as cyanide.

Components suitable for jewelry were made up consisting of low carbonsteel, copper and brass. Cleaning was carried on to remove grease,foreign matter and oxide as well known in the art according to 2 MetalsHandbook (8th ed. 1964) 307 and following.

The bath was heated to 100 F., plus or minus 0.5 F., maintained withinthat temperature range and constantly stirred. An insoluble anode(stainless steel) was used, at an anode to cathode ratio of 0.5: l. Thework was inserted as cathode and direct current was applied between theanode and cathode under a voltage of 1 to 1% volts and at a currentdensity of 15.0 amperes per square foot. The work was electroplated for60 seconds in the above bath under the above conditions and a depositwas obtained without burnishing which was silvery white and bright. Noporosity was visible and the coating was tar- 4 nish-resistant afterimmersion in concentrated sodium sulphide at 120 for 30 minutes.

Spectrographic analysis showed that the electrodeposit had the followingcomposition by weight:

Percent Cadmium 64 Silver 23 Nickel plus a small amount of impurityBalance EXAMPLE 2 Percent Cadmium 56 Silver 28 Nickel plus a smallamount of impurity Balance The thickness of the deposits obtained inthese cases were about 0.00001 inch. The deposits were subjected tosending and abrasion and were found to be adherent and resistant andsufficiently ductile to stand such treatment.

modifications to meet individual whim or particular need will doubtlessbecome evident to others skilled in the art to obtain all or part of thebenefits of my invention without copying the process and compositionshown, and I, therefore, claim all such insofar as they fall within thereasonable spirit and scope of my claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent as:

1. A tarnish-resistant bright ternary alloy essentially consisting of 50to by weight of cadmium, 20 to 31% by weight of silver, the balancebeing nickel and impurities.

2. An alloy of claim 1, essentially consisting of 56 to 64% by weight ofcadium, 23 to 28% by weight of silver, and the balance nickel andimpurities.

3. An alloy of claim 2, essentially consisting of 64% cadmium, 23%silver and the balance nickel and impurities.

4. An alloy of claim 2, essentially consisting of 56% cadmium, 28%silver and the balance nickel and impurities.

References Cited UNITED STATES PATENTS 2,182,380 12/1939 Hensel 151RICHARD O. DEAN, Primary Examiner

